Recently, there is an increasing need for air quality control such as sterilization and deodorization in a living environment, due to an increase in carriers of atopy, asthma, and allergic symptoms, and increased risk of infection such as seen in the explosive prevalence of new influenza. In addition, as living standards improve, an amount of food storage and a chance of storing leftover food are increased. Accordingly, the importance of environmental control in storage equipment such as a refrigerator is also growing.
In the related art intended to control air quality of a living environment, physical control as represented by a filter is generally used. According to physical control, relatively large dust and debris floating in the air may be captured, and bacteria, viruses, or the like may also be captured depending on the size of a filter hole. In addition, in a case that there are an immense number of adsorption sites such as in activated carbon, it may be possible to capture odor-causing molecules. However, there are problems in that air in a space to be controlled is required to evenly pass through the filter in order to capture these substances, the apparatus is increased in size, and maintenance costs such as filter replacement are also increased while having no effect on adhesive substances. Therefore, as a means to enable sterilization and deodorization of adhesive substances, it may be exemplified to release chemically active species in a space to be sterilized and deodorized. In spraying of chemicals or release of flavoring agents or deodorants, it is necessary to prepare the active species in advance and regular replenishment thereof is essential. On the other hand, a means to perform sterilization and deodorization using the chemically active species created by generating plasma in the atmosphere is increased in recent years.
Technologies to perform sterilization and deodorization by ions or radicals generated by discharge of plasma into the atmosphere may be classified into the following two types:
(1) a so-called passive type plasma generating apparatus in which bacteria and viruses floating in the atmosphere (hereinafter, referred to as “floating bacteria”) or malodorous substances (hereinafter, referred to as “odors”) react with ions or radicals within a limited capacity in the apparatus (for example, see Patent Document 1); and
(2) a so-called active type plasma generating apparatus in which ions or radicals generated by a plasma generating portion are released into a closed space (e.g., a living room, a toilet, a car interior, or the like) having a larger capacity than (1), and the ions or radicals react with floating bacteria or odors by a collision therewith in the atmosphere (for example, see Patent Document 2).
The passive type plasma generating apparatus of (1) has an advantage that high sterilization and deodorization effects may be expected because ions or radicals having high concentrations are created by generation of plasma in the small capacity. Meanwhile, the apparatus has a disadvantage that the size thereof is increased because floating bacteria or odors must be introduced into the apparatus, ozone as a common by-product of plasma generation is likely to occur, and a filter for adsorption or decomposition must be separately installed in order to prevent ozone from leaking out of the apparatus.
Next, the active type plasma generating apparatus of (2) has an advantage that the apparatus may be relatively small, and sterilization of bacteria (hereinafter, referred to as “adhesive bacteria”) adhered to a surface of clothing or decomposition of odors adsorbed onto the surface may be expected in addition to sterilization of floating bacteria or decomposition of odors in the air. Meanwhile, the apparatus has a disadvantage that only long-lived active species cannot help but expect sterilization and deodorization effects because ions or radicals are diffused within the closed space, which is very large compared to the volume of the apparatus, and have low concentrations. As a result, the deodorization effect may not be nearly effective in a space having a high odor concentration (a high concentration of 10,000 times that of active species).
From the above, in the passive type plasma generating apparatus, the effect is limited only to floating bacteria or odors contained in an air stream flowing into the apparatus. On the other hand, in the active type plasma generating apparatus, such effect cannot help but be expected only with respect to floating bacteria, adhesive bacteria, and odors having low concentrations. In other words, only either “sterilization and deodorization of floating bacteria” or “sterilization of floating bacteria and adhesive bacteria having low concentrations and deodorization of adhesive odors” may be realized using the related art.
However, there are some situations where sterilization of adhesive bacteria having high concentrations and deodorization of odors having high concentrations are required to be simultaneously performed in a daily life environment. The most typical example is a refrigerating chamber of a refrigerator in which many bacteria adhered to surfaces of food and a storage container surfaces exist and odors arising from food itself and decayed leftover food also exist.